Wheel cylinder seal assembly



June 1965 R. SHELLHAUSE ETAL 3,137,843

WHEEL CYLINDER SEAL ASSEMBLY Fil ed Nov. 19, 1962 1;" i0 L gg l l e 0/70GUS 3 BY can A. Bier/em 4 .4 wwmf The/r A/iame y United States Patent3,187,848 WHEEL CYLINDER SEAL ASSEMBLY Ronaid L. Shellhanse, Vandaiia,and arl A. Eieriem,

Kettering, Ohio, assignors to General Motors Corporation, Detroit, Mich,a corporation of Delaware Filed Nov. 19, 1962, Ser. No. 238,503 8Claims. (Cl. 188-452) The invention relates to a wheel cylinder assemblyin a wheel brake, and more particularly to the wheel cylinder boo-tconstruction and the method utilized in assembling the boot to the wheelcylinder. The invention also relates to the wheel cylinder assemblywherein the wheel cylinder boot is received internally of the end of thewheel cylinder and is held therein by friction and cohesive forces andmechanical locking en agement obtained by flowing the wheel cylinderboot material into the engaged surface of the wheel cylinder. A wheelcylinder assembly having this construction is advantageous in that itvirtually eliminates damage to the wheel cylinder boot during varioushandling operations prior to being assembled in a wheel brake, andprovides for better radiant heat dissipation While the brakes areoperating. Assemblies embodying the invention also provide better wheelcylinder boot retention characteristics which increase within a fewhours after installation and further increase after a short period ofuse under normal operating conditions. The boot retention and link pinforce-transmitting relation.

sealing characteristics are such that the boot link pin sealing sectionflips outwardly should an abnormal gas or fluid buildup occur behind theboot and within the wheel cylinder. This flippingyaction functions as asafety valve which will all-ow only a small fluid loss rather than acomplete fluid loss should the entire boot be forced away from the wheelcylinder. The sealing section will continue to have a sealing action inthe flipped condition. The internal position of the wheel cylinder bootalso permits better heat disispation characteristics by exposing theentire outer surface of the wheel cylinder to radiant heat beingradiated from the brake shoes during the braking operation instead ofhaving the wheel cylinder boot covering the cylinder end and therebyacting as a radiant heat insulator in this area and at the same timeabsorbing more heat than it does when inside the cylinder.

In the drawing:

'FIGURE 1 is a view of a portion of a wheel brake assembly embodying theinvention and having par-ts broken away and in section.

FIGURE 2 is a perspective view of a Wheel cylinder and boot in positionjust prior to installation of the boot in the cylinder, with partsbroken away and in section.

FIGURE 3 is an enlarged partial view having parts broken away and insection and showing somewhat sche-. matically the Wheel cylinder boot asretained in the end of the wheel cylinder.

The Wheel brake assembly may be of any suitable type and is illustratedin this instance as one of the duo-servo type. It includes a drum 10which is rotatableand to which the wheel is attached. A backing plate 12 is suitably attached to the vehicle. An anchor pin 14 is se cured tothe backing plate to receive and transmit the braking forces from theshoes 16 and 18 to the vehicle through the'backing plate. Shoes 16 and18 are mov- The wheel cylinder assembly 25 is secured to the backingplate 12 in force-transmitting and heat conducting relationship in anysuitable manner. The particular wheel cylinder assembly illustratedincludes a cylinder body 23 in which a cylinder bore 30 is formed. BoreGil is smooth finished by suitable operations such as honing, as is wellknown to those skilled in the art. Only one half of the interior of thewheel cylinder assembly 26 is illustrated in section since the other endof the assembly is substantially identical thereto but in reverserelation. The invention is also applicable to wheel cylinders of otherconstructions than those required for duo-servo brakes.

A piston 32 is operably received in the bore 30 and a cup seal 34engages the inner surtac-e of the piston and is retained in positionagainst the piston by spring seat 36 and spring 38. Piston 32 issuitably recessed as at 49 to receive link pin 42 so that the link pinend 44 remains substantially on the center line of the wheel cylinder.Link pin 42 extends out of the wheel cylinder so that its other end 46engages the web 48 of shoe 18 in This portion of the structure is'conventionalexcept for the ends of the cylinder body 28, one of whichis described below with regard to the wheel cylinder boot.

The wheel cylinder boot 50 is inserted in the end 52 of the cylinderbody 28 and is provided with an annu- V lar inner seal section 54 whichis in sealing engagement with the link pin 42. Boot 50 is preferablyconstructed somewhat like half of a hollow torus so that theintermediate body section 56 extends from the innerseal section 54 firstaxially in one direction relative to the outward of the inner'sealsection 54 and is formed as an'annula-r cylindrical section having anouter surface 60, an inner surface 62 and an end surface 64. 'The wheelcylinder boot is made of any suitable flexible material such as rubber,neoprene, styrene butadiene, or any elastomeric material having similarcharacteristics. Any material used must not be adversely afiected by thehydraulic brake fiuid utilized. It must also be able to withstandtemperatures in the area of 300 F. to 450 F. without melting, crackingor otherwise failing. It must be sufficiently flexible to permit theinner seal section 54 to move with pivotal movement of link pin 42 andto fiip outwardly under excess pressure within the permanently damaged.It must also be sufliciently strong to resist this flipping action untilsuch excess pressures are obtained. This, of course, is a function ofthe physical proportions of the boot, taking into consideration theother physical characteristics of the material utilized.

The boot St is preferably provided with aretainer ring .66 which can bebonded to the inner surface 62, or may otherwise be secured thereto. Ifdesired the inner surface 62 may be the bottom of a shallow recess whichhas approximately the thickness of the retainer ring 66.

so that the retainer ring is positioned against a boot shoulder 68 andits edge 70 is substantially in alignment ably mounted on the backingplate in the usual manner so that they are movable into and out ofbraking engagement with the drum ll). Suitable retractor springs 20 and22 are secured to the anchor pin 14 in the usual manner so that theyperform their usual functions, includingretention of the guide plate 24in place on the anchor pin.

with the endsurface 64 of the boot.

The recess 72 formed in the end 52 of the wheel cylinder preferably hasa greater diameter than the bore 33 so that a shoulder '74 is provided.The surface 76, which is the bottom of the recess 72, has a controlledfinish which is provided with a predetermined roughness. Where thefinish of bore 30 is honed to approximately a 15 micro-inches R.M.S.finish, surface 76 is finished so that it has a 60 tol20 micro-inchesR.M.S.

finish. This range is given here as indicative of the roughness but isnot so critical that the roughness must be maintained within these exactlimits. It has been found, however, that these limits yield satisfactoryresults without requiring the close control in the finish operationwhich is required in finish bore 30. The illustration in FIGURE 3indicating the roughness of this surface is for illustrative purposesonly and is not indicative of the precise roughness desired. 7

The wheel cylinder, boot St is installed in the recess '72 by pressingit'axially inward. A lubricant such as diacetone alcohol or a glycolether such as commercially available brake fluid may be used. Thelubricant must assist in the installation without being so slippery thatthe immediate friction and cohesive interaction of the wheel cylinderbody and the boot is insuflicient to resist the outward force exerted onthe boot by spring 38 through cup 36 and piston 32. Also, the lubricantmust'be compatible with the material of which the boot is made. Sincethe boot outer cylindrical surface 60 is preferably provided with adiameter so that it is a slight interference fit in recess 72, thematerial of which the boot is made is slightly compressed uponinstallation. The boot is pressed axially into the recess;72, and by wayof example, in a wheel cylinder the installation force has been found tobe from 10 to 20 pounds. The boot is held in place by frictionalengagement of its surface 60 with the controlled finish surface 76immediately upon installation, and this frictional engagement dependentto some extent on the force exerted radially outward due to theinterference fit. These forces are augmented by the relative stiffnessof the retainer ring 66 which resists radial collapse of the wheel bootand therefore exerts a reaction force radially outward against the wheelcylinder body tending to compress the boot section 58. It has been foundthat exposed to them in radiant heat relation.

l compressed for long periods of time. This set in the section 58 of theboot does not decrease the removal forces required after some months,for example. It is thought that this set is counteracted by theeffectiveness of the cohesive and mechanical lock of the surfaces 60 and'76.

It has been found that at times the shoe web temperatures will be ashigh as 850 F. for short periods when the brakes are temporarilyoverloaded. The heat is radiated from the drum and the shoes to thebacking plate, the wheel cylinder, the reactor springs, and any otherelements In previous commonly used wheel'cylinder constructions thewheel cylinder boots were made sufiiciently large to be fitted tightlyover the outside of the wheel cylinder ends. This construction istypical of all current production brakes of the duo-servo type. In thisconstruction the ends of the wheel cylinder, which are the-parts of thewheel cylinder bodies closest to the shoe webs, are insulated by theboots. Thus the wheel cylinder cannot function as a heat sink and heattransfer member wherein it receives the radiant heat from the shoes andtransmits it to the backing plate. Instead the outer peripheries of thewheel cylinder boots receive extreme amounts of radiant heat underextreme brake conditions and tend to hold it without transferring it.This causes them to crack and fail prematurely. This also results inless net heat removal from the brake shoes in a given unit of time, thiscontributing to the tendency of the brakes to fade since they reach andretain higher shoe temperatures at an earlier point in time. By use ofthe structure embodying the invention however, the entire outer surfaceof the wheel cylinder body 28 is exposed to radiant heat from the shoewebs and, commonly being made of cast iron, readily absorbs this heatimmediate removal of the boot after such installation a can beaccomplished by exerting a removal force axially against the retainerring 66 whichis approximately half of the'installation force. Thus'atthis time the removal force is only required to overcome the frictionalforce plus a slight cohesive action. However, if the boot is permittedto set for a time without further work being done on or by the assembly,a removal force approximately equal to the installation force isrequired. This has been found to be caused by the flow of the materialof which the boot is made at and near surface 60 into the controlledroughness surface 76 so that these surfaces are mechanically locked;This is illustrated in FIGURE 3 in a nonscale presentation. This flowcondition can be accelerated appreciably by exerting radial forcesagainst the retainer ring66 so as to cause the surface 60 of the boot toflow morequickly into complementary engagement with the controlledfinish surface 76. This may also be accomplished by using the wheelcylinder at normal brake operating temperatures for a short period oftime. It has been found for example that after such usage the removalforce required is approximately double or triple the installation force.It is believed that this occurs due in part to. a cohesivereactionbetween the cylinder and the boot. It may also be due in part to somepressures being exerted internally of the wheel cylinder boot in thechamber 73 formed by the boot, the-piston 32, the link pin 42, and thecylinder body 28. These pressures are obtained by normal movement of thepiston 32 in the bore 30 which alternately decreases and increases thevolume of chamber 78. The

and transmits it to the backing plate so that the boots are protectedfor an additional period of time. This also tends to decrease the fadetendency of the brakes since the heat is not retained as long as before.Also the wheel cylinder boot does not have its relative section exposedto the extremely high radiant temperature, but to a lesser temperaturefound in the wheel cylinder body ends, therefore decreasingthelikelihood of failure of the boot. In the particluar mechanism embodyingthe invention it is preferable to have all of the annular cylindricalouter heating of the wheel cylinder boot under operating conditions, aswell as the heating of the cylinder body, also contributes to the fullmechanical lock condition of the boot. Heat at or below the normaloperating temperature range of the boot, and therefore above ambienttemperatures can therefore be used to accelerate the mechanical lockcondition, 'or in conjunction with the radially outwardforces notedabove, or independently'of them. It is well known that elastomermaterial such as those of which boots may be made. suffer a compressionset when peripheral section 58 of the boot shielded by the end of thewheel cylinder. Thus decreasing the radiant heat exposure of the boot toa minimum while permitting it to operate in the usual manner.

Another particularly important advantage of the in- V vention isobtained after assembly of the wheel cylinder unit and during handlingthereof. In prior construction units wherein the boot was cut over thecylinder end, the boot would be almost invariably out. If .the wheelcylinder was dropped from a height of approximately one foot to a solidsurface such as a concrete-floor, a work bench, or table, etc., this cutmay be relatively minute in many instances but forms a weak spot wherehigh stresses occur and becomes the direct cause of premature bootfailure. By' placing the boot inside the wheel cylinder end ascontemplated in accordance with the invention,

handling damage to theboot is eliminated. The wheel cylinder embodyingthe invention can be dropped from a height of five feet on most types ofsurfaces, including edges of machinery, benches, tables, etc., as wellas concrete floors without damage to the unit. In particular no cutsoccur on the boot. This is an extremely important advantage in themanufacture of wheel cylinder assemblies since such assemblies arehandled by hand or machinery numerous times after being puttogether','not the least of which is the handling of replacement'wheelcylinders by mechanics in all types of garages.

* We claim: I V

1. A brake wheel cylinder assembly comprising, a housing having acylinder bore provided therein, a piston operable in said bore andforming therewith fluid pressure chamber, one end of said housingadjacent said cylinder having a cylindrical recess formed therein oflarger diameter than said cylinder bore whereby a shoulder is provided,the annular inner surface of said recess having a predeterminedcontrolled micro finish of greater roughness than said cylinder bore, alink pin in engagement with said piston and extending through and beyondsaid cylinder for actuation of a brake shoe, and an annular wheelcylinder boot received about said link pin in sealing engagementtherewith and having a cylindrical outer periphery inserted in saidrecess and in cylindrical surface engagement with the surface thereofwhereby said boot is micro-mechanically retained and the end of saidwheel cylinder is radially outward of the cylindrical outer periphery ofsaid wheel cylinder boot.

2. A Wheel cylinder assembly having a recessed cylindrical end with theinner surface thereof having a controlled micro finish within apredetermined roughness range, a flexible wheel cylinder boot having anannular inner seal section for sealing engagement with a link pin and anannular cylindrical outer seal section extending axially parallel tosaid wheel cylinder and received within said recess whereby the outercylindrical surface of said outer seal section engages the controlledroughness surface of said recess by a micro mechanical lock created bymaterial flow of said wheel cylinder boot to conform with the controlledrough surface, the micro-mechanical lock providing the means holdingsaid boot in said cylindrical end.

3. Mechanism for increasing radiant heat dissipation and providingmicro-mechanical locking boot retaining means in a wheel brake assemblyhaving a brake drum and a backing plate with brake shoe means movablymounted thereon and providing a radiant heat source when actuated intobraking engagement with said drum, said mechanism comprising a wheelcylinder assembly adapted to be secured to said backing plate in heattransmitting relation and having a cylinder and piston and link pinmeans for actuating said brake shoe means and Wheel cylinder boot meansreceived internally of said cylinder in sealing and micro-mechanicallocking relation therewith and in sealing relation with said link pinmeans whereby the entire outer surface of said cylinder is in heatradiating relation to said shoe means to effectively receive radiantheat therefrom for primary heat transmittal to said backing plate andsecondary heat transmitted to said boot means toincrease saidmicro-mechanical locking relation and to protect said boot means fromreceiving radiant heat from said shoe means by shielding a part of saidboot means therefrom.

4. A wheel cylinder assembly comprising a body having a cylinder boreopening through atleast one end thereof with said bore having a firstsection and a second section, the wall of said first bore section havinga micro finish of predetermined controlled quality on the order ofmicro-inches R.M.S. and the Wall of said second bore section having arougher micro finish and adjacent the open bore end with no parts of thewall of said second bore section having a radius less than the radius ofany part of the wall of said first bore section, a piston movablyreceived in said bore end working in said first bore section, and arubber-like boot received in said bore and having an outer cylindricalsection in cylindrical surface engagement with the wall of said secondbore section, said boot outer cylindrical section having boot materialflowed radially outward in complementary relation to the micro finishsurface of the wall of the second bore section and cooperating therewithto establish a mechanical lock between said boot and said second boresection.

5. A fluid pressure servomotor comprising a cylindrical body having aninner cylindrical first wall with a micro finish wall surface anddefining a pressure chamber cylinder and a power wall movable in saidbody, a cylindrical opening at least one end of said body through whichsaid power wall may be removed and replaced, said body further having aninner cylindrical second wall with a predetermined controlled microfinish wall surface rougher than the micro finish of the first body wallwith the minimum radius of any part of the second wall surface beinggreater than the maximum radius of any part of the first wall surface,and a flexible seal having a cylindrical outer surface engaging saidsecond wall surface in mechanical micro-interlocking relation.

6. The servomotor of claim 5, said seal having means urging thecylindrical outer surface thereof radially outward thereby enhancing themicro-interlocking relation between the seal and the second wallsurface.

7. The servomotor of claim 6, said cylindrical body having a shoulder atthe juncture of said first and second walls and receiving the inner endof said flexible seal thereagainst.

S. A pressure actuated cylinder and piston assembly having a body formedwith a cylinder with at least one open end, said cylinder being definedby a wall having a piston-receiving micro finish inner wall section anda seal-receiving outer wall section adjacent and extending to thecylinder open end having a micro finish substantially rougher than theinner wall section and a radius greater than the radius of the innerwall section, the cylinder body at the outer wall section having athickness less than the wall thickness of the body at the inner wallsection, a piston operating in said cylinder and forming a movablepressure chamber wall, force-transmitting means in operative associationwith said piston and extending axially outwardly of said cylinder, andannular seal means having an inner annulus sealing about saidforce-transmitting means and a cylindrically formed outer annulus havingan inner radius at least as great as the radius of said inner wallsection and an outer cylindrical surface the radius of which issubstantially equal to the radius of said outer wall section, said outercylindrical surface of said seal means outer annulus being in microsurface interlocking engagement with said outer wall section.

References Cited by the Examiner UNITED STATES PATENTS 3,003,973 6/35Oliver 60-546 2,120,922 6/38 Rasmussen 6054.6 X 2,354,831 2/44 Rike74-18.2 2,442,640 6/48 Dunn 29-451 2,544,541 3/51 McCarthy et al 7418.22,924,008 2/60 Haushalter 29-451 2,938,349 5/60 Britton 60-546 3,043,3387/62 Hanson 74-182 X EUGENE G. BOTZ, Primary Examiner.

ARTHUR L. LA POINT, DUANE A. REGER,

Examiners,

3. MECHANISM FOR INCREASING RADIANT HEAT DISSIPATION AND PROVIDINGMICRO-MECHANICAL LOCKING BOOT RETAINING MEANS IN A WHEEL BRAKE ASSEMBLYHAVING A BRAKE DRUM AND A BACKING PLATE WITH BRAKE SHOE MEANS MOVABLYMOUNTED THEREON AND PROVIDING A RADIANT HEAT SOURCE WHEN ACTUATED INTOBRAKING ENGAGEMENT WITH SAID DRUM, SAID MECHANISM COMPRISING A WHEELCYLINDER ASSEMBLY ADAPTED TO BE SECURED TO SAID BACKING PLATE IN HEATTRANSMITTING RELATION AND HAVING A CYLINDER AND PISTON AND LINK PINMEANS FOR ACTUATING SAID BRAKE SHOE MEANS AND WHEEL CYLINDER BOOT MEANSRECEIVED INTERNALLY OF SAID CYLINDER IN SEALING AND MICRO-MECHANICALLOCKING RELATION THEREWITH AND IN SEALING RELATION WITH SAID LINK PINMEANS WHEREBY THE ENTIRE OUTER SURFACE OF SAID CYLINDER IS IN